1. Field of the Invention
The present invention relates to a lithium ion battery control system controlling charging and discharging of a lithium ion battery.
2. Background Art
Since they have a high energy densities, lithium ion batteries have attracted attention as batteries used in vehicles such as railroad cars and automobiles or used to store power generated through photovoltaic power generation or wind power generation and to supply the power to power systems. For example, when a lithium ion battery (hereinafter, appropriately referred to as “battery”) is mounted on a vehicle, examples of such a vehicle include zero-emission electric vehicles without an engine mounted, hybrid electric vehicles with both an engine and a rechargeable battery mounted, and plug-in hybrid electric vehicles charged directly from a system power source. Such batteries are expected to be used in a stationary power storage system supplying power at the time of emergency in which a normal power supply system is out of order.
Superior durability is required for batteries for such various uses. For example, even when the environmental temperature is raised or a charging-discharging cycle is repeated, it is necessary that the decreasing rate of rechargeable battery capacity (that is, battery capacity) is low and the retention rate of the battery capacity is high for a long period of time; The conservation characteristics and the cycle life, for example, under high-temperature circumstances of 60° C. or higher becomes significant requirements due to radiant heat from the road surface or heat conduction from the interior of the vehicle.
However, in the lithium ion batteries, a degradation in battery capacity is caused by exposing the lithium ion batteries to high-temperature circumstances or performing charging-discharging cycles on the lithium ion batteries. The degradation in capacity becomes marked when the lithium ion batteries are exposed to high voltages or the cycle is performed with a wide voltage range or with a large current.
In consideration of such situations, for example, JP-2008-192607 discloses a degradation suppressing method of calculating a degraded state (SOH: State Of Health) from a difference between a charging-discharging cutoff voltage and an open circuit voltage after the charging-discharging and changing the charging-discharging time and the charging-discharging cutoff voltage on the basis of the calculated SOH.